1. Field of the Invention
The disclosed technology relates to a sense amplifier for amplifying a low swing voltage signal, and further relates to an electronic memory such as SRAM, DRAM, FLASH comprising such a sense amplifier.
2. Description of the Related Technology
Sense amplifiers (SAs) are used widely in digital circuits for a number of applications including SRAM, DRAM. The purpose of a sense amplifier is to detect a small input signal such as e.g. a small voltage difference between two bitlines of a static random access memory (SRAM), and to amplify the difference signal to a full swing voltage (e.g. VSS or VDD). One of the most important metrics for a sense amp is the input referred offset. The differential input voltage must exceed this input referred offset in order to cause the sense amplifier to amplify the input signal to the correct large swing value at its output.
Continued process scaling tends to cause increases in the input referred offset of sense amplifier topologies. This is largely due to the overall increase in process variation due to mechanisms such as lithographic variation and random doping fluctuation (RDF). These local variations cause the threshold voltage (Vt) of transistors with identical layout to be distributed normally, and the standard deviation of the Vt distribution is proportional to 1/√(WL) (Pelgrom's law). Differences in the threshold voltage will lead to increased input referred offset for the SA.
One possible solution for building a reliable sense amplifier (SA) as technology scales, is the upsizing of the transistor sizes of the sense amplifier, but this is a very energy expensive solution. Sense amplifier calibration is a family of techniques that aims to solve the sense amplifier mismatch offset problem enabling a low input swing sensing without increasing the energy consumption and the sensing delay. Calibration techniques as described in [1]-[6] are quite effective, but for many applications, the introduction of a separate calibration phase is not acceptable. Every test vector applied to calibrate the sense amplifier increases the test cost and test time. This inhibits the advantages offered by the calibration techniques and is not an option for low energy system on chip (SoC) designs.